Treatment of wood



M. G. SNELLING TREATMENT OF, WOOD Filed Jan. 27. 19:4

W W fi/w INVENTOR BY Q. MM,

" ATTORNEY Patented Dec. 17, 1935 Marjorie G. Snelling, Allentown, Pa, Application'January 27, 1934, Serial No; 708,579

10 Claims.

My invention relates to improvements in methods of treating wood and more particularly relates to improved means of surfacing or finishing wood for use in cabinet making or for any other purpose. One of the objects of my invention is to provideimproved means for surface-treating wood by which thecost of the finished wood prodnot can be materially reduced through lessening the number of operations required to produce a satisfactory finish on the article, while another object-of my invention is reducing the time required to produce a satisfactory permanent finish on wood surfaces. Still another object of my invention is to provide means by which the appearance of the treated wood surface is permanently improved, and the resistance of the treated wood surface to atmospheric and other agencies is permanently increased.

I have discovered that certain liquid chemical agents such as dilute acid and dilute alkali alone or imbuffered solutions are readily taken up by smooth or planed surfaces of wood, and that such reagents exert a remarkable selective swell,- ing action on the bundles of fibres which form the xylem or wood, having little or no action on the more compact or denser fibre groups, but exerting a very marked swelling action on the less dense and more porous fibre groups or aggregates. By moistening the surface of a smooth surface of wood with a suitable reagent having a pH value either higher or lower than that of pure water, or having high osmotic pressure as compared with water, this swelling effect occurs. Water produces a slight differential swelling-effect upon I some woods that are not entirely neutral in pH value, but is without effect upon other woods, and

particularly wood of neutral pH and all the harder woods that are ofprincipal value in cabinet making. All acids, both organic and inorganic, and all alkalies, both fixed and volatile, show a differential swelling effect, although in different measure. I find that dilute solutions of formic, acetic,

propionic, butyric, citric, tartaric, hydrochloric,-

sulfuric, nitric, trichloracetic, malic, boric, sulfur.- ous, oxalic and many other acids produce this characteristic effect, and the great number of acids which show this swellingeifect is best explained by thetheory that the action is dueto osmotic pressure produced by a pH value sufllciently difierent from the normal relatively neutral condition of the wood to cause the observed swelling of the colloidal matter forming the cells which make up the softer portion of the wood.

Just as all acids produce: a. selective swelling of the softer groups of Wood fibres as compared with the harder groups of wood fibres, so all ,alkalies,

including ammonium hydroxide, and many acid and basic salts,produce a similar swelling. Assome reagents color or otherwise harm the wood, I prefer to use certain specific reagents, and particularly a solution containing from 2% to 10% of acetic acid and from 2% 'to 10% of citric acid. I am fully aware, however, that the swelling which I have observed may be produced by a wide variety of reagents, including all water soluble acids and all water soluble alkalies, and a greatnumber of salts, particularly the ammonium and alkali salts of formic, acetic, citric and tartaric acids, and

the alkali and ammonium salts of sulfurous, thiosulfuric and hyposulfurous acids. The observed swelling is not confined to thesespecific reagents. however, and satisfactory swelling may also be obtained from 2% to 30% aqueous solutions of stannous chloride, zinc chloride, sodium potassium tartrate, and many other like water-soluble salts of relatively low molecular weight.

ploy concentrations of my reagent varying from 5% to 15%, but my preferred reagent is a solution containing 5% of acetic acid and 5% of citric acid.

I apply my reagent to the smooth, planed or sand- 25 ed surfaceof the wood by means of a spray gun. or by a brush, or by dipping the wood in the reagent, or in any other convenient way, and I then allow a period of from one-half hour to five or six hours to elapse, within which the selective 30 swelling of the softer fibre groups occurs.

When the softer fibre groups have reached a condition ofmaximum swelling the reagent begins to dry, but for some reason unknown to me the selective swelling of the fibre groups is not 35 reversible, and the treated wood retains even after complete drying the roughened surface which resulted from the selective swelling of the softer fibre groups. I next subject the surface of the wood, roughened in the manner described by the selective swelling of the more porous and softerfibre aggregate groups, to an operation which has as its purpose the removal by tearing, cutting or abrasion of all portions of the wood which are swoll'en beyond the original plane represented by 5 or with any other satisfactory abrading or smooth- 5o ening means,- the object of the treatment being to completely remove by cutting or abrasion all the portions of the wood fibres which now stand out beyond the original smooth surface of the wood,

The result of this treatment is to leave a In the preferred practice of my invention I em- 20 vless compact fibre groups. v

holic solution of shellac forms a desirable insmooth surface of wood made up in part of the original unswollen groups of dense fibre aggregates, and made up in part of the swollen and expanded remnants of the original fibre groups of low density. One characteristic result-of my treatment is that, instead of increasing the density of the softer groups of fibre elements, or of decreasing the density of the harder groups of fibre elements, I leave the harder and denser groups of fibre elements substantially unchanged, while I soften, swell and then remove part of the softer and more porous groups of fibre elements, and as a consequence the wdod which has been treated by my process shows a greater difference between its harder and its softer fibre elements than were shown before the treatment was applied.

I next apply to the entire surface of my treated wood a protecting coating of an indurating compound, that is capable of selectively penetrating the surfacial fibre groups. As a result of the effect of the preceding treatments as described, this indurating reagent will be absorbed in the least quantity by the originally dense or compact fibre groups, and it will be absorbed in much greater measure, or in much greater quantity, by the softer and more porous remaining portions of the originally softer and less dense or An ordinary alcodurating reagent, the shellac being left within the cells of the wood after evaporation of the solvent, or an aqueous solution of shellac inammonia water or borax may be used. Varnish, and particularly lacquer varnishes containing natural or synthetic shellac substitutes or natural resins, resinoids or resin substitutes may be employed, a very wide variety of indurating reagents being entirely suitable to the practice of my invention, and the choice of a suitable indurating agent, either primary or secondary, being largely determined by the purpose for which the wood is tobe used whether indoor or outdoor, and if outdoor, the degree of resistance to atmospheric agents which is desired. I may,

for example, treat the wood with an indurating agent and subsequently alter this indurating agent by heat or by the action of a chemical agent, for the purpose of further hardening the induratingagent. I have even found that such indurating agents as aqueous solutions of natural gums, and particularly aqueous solutions of acacia, tragacanth and the like may be employed, although alkaline or alcoholic solutions of shellac,

rosin, resins and synthetic resins form the most satisfactory indurating agents.

Summarizingthe treatment described, I first soften and swell the softer and less resistant fibre groups, without correspondingly softening or swelling the harder, denser and more resist ant fibre groups. I next abrade and remove the softened and. swollen upper portions of the initially softer and less dense fibre groups, without correspondingly removing any portion of the harder and denser fibre groups, and I finally apply anindurating agent which is selectively absorbed by the initially softer and selectively .softened and swollen fibre groups, without such reagent being equally absorbed by the denser or less porous fibre groups, and as a final result of my process I obtain a surface which, is equally hard and resistant over its entire area, through the indurating effect being much greater in the initially softer and subsequently further softened portions than it was inthe initially harder and pendicular to the direction of the fibre groups 10' making up such piece of wood. can represents. the upper surface portion of the harder, denser and more resistant fibre groups, while bbb represents the upper surface portion of the softer, more porous and less dense and less resistant fibre 15 groups and aggregates.

Figure 2 is a similar transverse section through the same piece of wood represented by Figure 1,

after the upper or surface portions of thesofter, more porous, less dense and less resistant fibre 20 groups have been swollen as shown at ccc by'the action of a swelling agent as described. Figure 3. is a similar transverse section through the piece of wood represented by Figure 1 and Figure 2, after the raised portions of the softer fibre 25 groups ccc have been removed by cutting or abrasion, to leave the still less dense and more porous surface portions ddd. Figure 4 is a similar transverse section through the piece of wood represented by Figures 1, 2 and 3, after an in- 80 durating agent has penetrated into the softer fibre groups to vary.ng extents and varying depths determined by the porosity of the fibre groups that has been caused or induced as a result of the treatment'described.

It will be evident that the wood, treated as described, may subsequently be covered by any desired type of protecting film, such as paint, varnish, lacquer or the like. Very extensive tests have proven that wood, treated as described, of- 40 fers greater res'stance to both atmospheric agencies and mechanical wear, than wood treat-- ed by the usual finishing processes. Where stains are applied to the woods, a materially increased contrast effect is produced, due to the 45 greater absorption of the stain in the softened fibre groups, the stain being preferably applied after the removal of the upper swollen portions of the fibre groups,,and before the application of the indurating reagent. .60

My invention may be applied with substantially equal success-to all of the, customary types of hard and soft woods used in cabinet making and for like purposes. Although my invention is of maximum usefulness in the case of woods which 55 show the greatest contrast between the softer fibre groups and the harder fibre groups, my invention may be applied to all woods with some benefit, since, I have found that in every wood there are differences in the hardness and density of, some of the longitudinal or transverse fibre groups as compared with other fibre groups, and the effect of my invention is to improve the surface strength of wood by rendering uniform the strength of the fibre groups which make upjthe surface, by preferentially strengthening or indurating the softer fibre groups as compared with the initially harder or denser fibre groups in the manner described.

.It will be noted that the effect of the swam-m I versely proportional to the density of the wood, however, as I find that dense fibre groups do not swellat all. or swell to so slight an extent as to be unnoticeable, while very porous fibre groups or aggregates expand and swell quite disproportion-- ately to their relative densities. My process removes all of the expanded fibre groups that extend beyond the original plane of the wood, but I do not remove those portions of the fibre groups which, in their expanded condition, lie beneath the original plane of the wood. In my indurating step. I find that my indurating fluid'is taken up by the expanded fibre group aggregates to a greater extent the lower the density of the fibre aggrewould be represented by the proportionality of the densities of the fibre groups.

As a result of this peculiar distribution of expansion or swell ing. and of the absorption of the indurating fluid,

I obtain as my final product a remarkable uniformity in the hardness of the fibre groups or aggregates, which is quite different from any efiec ever obtained or discribed in the prior art.

If desired, I may prolong the action of my chemical swelling agent, in the first stage of my process, eitherby repeated applications of the swelling reagent, or by applying dampened cloth or damp paper, or wet sand over the surface, or by otherwise modifying the humidity of the air in contact with the surface that has been treated; In general I find, however, that when I use a dilute soution of acetic acid, or preferably a dilute solution of acetic acid and citric acid, a single application of the reagent produces entirely satisi factory swelling action, and no special control of humidity in the treating room is necessary;

When swelling agents are used which discolor the wood, or which have any other harmful effect upon the wood, I may, after the swelling treatment and after the following abrading treatment, remove or neutralize the swelling agent. I find that washing with water sufiiciently removes most solutions of acid and basic salts which otherwise have a satisfactory swelling action, and alkali hydroxide, and any reagent which might produce 7 an efilorescence from contact with the air, may be chemically neutralized or may be removed from the wood by washing. I am mentioning these possibilities for the purpose of making a complete disclosure, but in the application of my invention I find that the simplest treatment is the best, and a solution of from 2% to 10% of a volatile acid and particularly of acetic acid, with from 2% to 10% of a solid acid such as citric acid, tartaric acid, or a mixture of two volatile acids such as acetic acid and trichloracetic acid, gives such extremely satisfactory results that it is not necessary or desirable to employ other materials such as sulfuric acid, for example, which may in time cause some harmful action on the wood, or to employ solutions or salts that might in time have a damaging effect upon either the wood itself or on the overlying protecting films of paint or varnish which may be later applied.

In view of the very wide choice of indurating agents which I may employ, broadly comprising any satisfactory solid natural or synthetic resin or resin-like substance, it is undesirable to name a wide variety of materials, .and I find that ordinary shellacis an almost ideal indurating agent for my purpose, although many other natural and synthetic resins may be employed, particularly in be further hardened if desirable by suitable heat 5 connection with very hard woods, where a very hard indurating agent is necessary to equal the hardness of the harder fibre groups. It will of course be evident that my indurating agent may treatment, and this is' particularly effective when using some of the newer synthetic resins which polymerize spontaneously with time, or under the cordance with myfinven'tion.

It will be evident that many changes may be made in the process as described without departing from the essential principles of my invention as herein described, and accordingly no limitations should be placed upon my invention except as indicated in the appended claims.

I claim:

1. The-process of treating wood which com- 20 prises exposing a smooth surface of wood to a selective swelling reagent to swell the softer fibre groups to a greater extent than the harder fibre groups, restoring a smooth surface to the wood by removing all portions. of'the swollen fibre 25 groups which extend beyond the original plane surface of the wood and selectively filling the fibers at the surface of the wood with an indurating material which penetrates the softer swollen fibre groups more readily than the initially harder 30 and subsequently unchanged fibre groups. 2. The process of treating wood which comprises exposing a smooth surface of wood to a selective swelling agent comprising an acid to swell the softer fibre groups to a greater extent than the harder fibre groups, restoring a smooth surface to the wood by removing all portions of the swollen fibre groups which extend beyond the original plane' surface of the wood and selectively filling the fibres at. the surface of the wood with a resinous indurating material which penetrates the softer swollen fibre groups more readily than the initially harder and subsequently unchanged fibre groups.

3. The process of treating wood which com- 45 prises exposing a smooth surface of wood to a selective swelling agent comprising. a volatile. acid to swell the softer fibre groups to. a greater extent than the harder fibre groups, restoring a smooth surface to the Wood by removing all portions of the swollen fibre groups which extend beyond the original plane surface of the wood and selectively filling the fibres at the surface of thewood with a resinous indurating material which penetrates'the softer swollen fibre groups more 55 readily than the initially harder and subsequently unchanged fibre groups.

4. The process of treating wood which comprises exposing a smooth surface of wood to a reagent having a pH value sufficiently different from the pH value of the wood being treated to induce swelling of the softer fibre groups present in the wood, restoring a smooth surface to the .wood by removing all portions of the swollen fibre groups which extend beyond the original plane surface of the wood and therafter selectively indurating the remaining portions of the swollen fibre groups at the surface of the wood by t eatment with a resinous impregnating agent.

'5. The process of treating wood which comprises exposing a smooth surface of wood to a selective swelling agent comprising a volatile acid and a non-volatile acid to. swell the softer fibre groups to a greater extent than the harder fibre. groups, restoring a smooth surface to the wood by storing a smooth surface to the wood by removing all portions of the swollen fibre groups which extend beyond the original plane surface'of the wood and selectively filling the fibres at the sur-.

face of the wood with a resinous indurating material comprising shellac which penetrates the softer swollen fibre groups more readily than the initially harder and subsequently unchangedfibre groups. l I

'7. The process of treating a smooth surface of wood which comprises decreasing the density of the fibre groups of lower density on such surface,

without correspondingly changing the density of the fibre groups of higher density by means of a chemical swelling agent, removing a portion of the fibre groups of lower density projecting beyond the original surface without removing a corresponding part of the fibre groups -of higher density, and impregnating the fibre groups of lower density with an indurating agent without correspondingly impregnating the-fibre groups of higher density.

'8. The process of treating a smooth surface of wood which comprises applying a chemical swelling agent to decrease the density ofthe fibre groups of lower density on such surface without correspondingly changing the density of the fibre groups of higher density, removing a portion of the fibre groups of lower density projecting be,-" yond the original surface without removing a corresponding part of the fibre groups of higher density, and impegnating the fibre groups of lower density with a solid indurating agent without correspondingly impregnating the fibre groups of higher density. 19

9. The process of treating wood which comprises exposing asmooth surface of wood to a selective swelling reagent to swell the softer fibre groups to a greater extent than the harder fiber groups, restoring a smooth surface to the wood by removing all portions of the swollen fiber groups which extend beyond the original plane surface of the wood and selectively filling the fibers at the surface of the wood with a finishing protecting material which penetrates the softer 20 swollen fiber groups more readily than the initially harder and subsequently unchanged fiber' groups.

10. The process of treating wood which comprises-exposing a smooth surfaceof wood to a reagent having a pH value sufiiciently different rom the pH value of the wood being treated to induce swelling of the softer fiber groups present in the wood, restoring a smooth surface to the wood by removing all portions of the swollen fiber groups which extend beyond the original plane surface of the wood and thereafter selectively impregnating the remaining portions of the swollen fiber groups at the surface of the wood by treatment with a finishing protecting agent.

MARJORIE G. SNELLING. 

